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Enterprise JavaBeans 3.1, 6th Edition
book

Enterprise JavaBeans 3.1, 6th Edition

by Andrew Lee Rubinger, Bill Burke
September 2010
Intermediate to advanced content levelIntermediate to advanced
766 pages
18h 35m
English
O'Reilly Media, Inc.
Content preview from Enterprise JavaBeans 3.1, 6th Edition

Named Queries

Java Persistence provides a mechanism so that you can predefine JPA QL or native SQL queries and reference them by name when creating a query. You would want to predeclare queries for the same reason you create String constant variables in Java: to reuse them in multiple situations. If you predefine your queries in one place, you have an easy way to fine-tune or modify them as time goes on. The @javax.persistence.NamedQuery annotation is used for predefining JPA QL queries:

package javax.persistence;

public @interface NamedQuery {
   String name( );
   String query( );
   QueryHint[] hints( ) default {};
}

public @interface QueryHint {
   String name( );
   String value( );
}

public @interface NamedQueries {
   NamedQuery[] value( );
}

You use the @javax.persistence.NamedQueries annotation when you are declaring more than one query on a class or package. The @javax.persistence.QueryHint annotation declares vendor-specific hints. These hints work in the same way as the Query.setHint() method described earlier in this chapter. Here’s an example:

@NamedQueries({
   @NamedQuery
(name="getAverageProductOrderAmount",
               query=
                 "SELECT AVG( o.amountPaid )
                  FROM ProductOrder as o")
})
@Entity
public class ProductOrder {...}

This example declares a JPA QL query on the ProductOrder entity bean class. You can then reference these declarations in the EntityManager.createNamedQuery() method:

Query query = em.createNamedQuery("getAverageProductOrderAmount");

Named Native Queries

The @javax.persistence.NamedNativeQuery ...

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Publisher Resources

ISBN: 9781449399139Errata Page